 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/

 package org.eclipse.core.commands.common;

 import java.util.HashMap ;
 import java.util.HashSet ;
 import java.util.Iterator ;
 import java.util.Map ;
 import java.util.Set ;

 /**
  * <p>
  * A manager of {@link HandleObject} instances. This has some common behaviour
  * which is shared between all such managers.
  * </p>
  * <p>
  * Clients may extend.
  * </p>
  *
  * @since 3.2
  */
 public abstract class HandleObjectManager extends EventManager {

     /**
      * The set of handle objects that are defined. This value may be empty, but
      * it is never <code>null</code>.
      */
     protected final Set definedHandleObjects = new HashSet ();

     /**
      * The map of identifiers (<code>String</code>) to handle objects (
      * <code>HandleObject</code>). This collection may be empty, but it is
      * never <code>null</code>.
      */
     protected final Map handleObjectsById = new HashMap ();

     /**
      * Verifies that the identifier is valid. Exceptions will be thrown if the
      * identifier is invalid in some way.
      *
      * @param id
      * The identifier to validate; may be anything.
      */
     protected final void checkId(final String id) {
         if (id == null) {
             throw new NullPointerException (
                     "A handle object may not have a null identifier"); //$NON-NLS-1$
 }

         if (id.length() < 1) {
             throw new IllegalArgumentException (
                     "The handle object must not have a zero-length identifier"); //$NON-NLS-1$
 }
     }

     /**
      * Returns the set of identifiers for those handle objects that are defined.
      *
      * @return The set of defined handle object identifiers; this value may be
      * empty, but it is never <code>null</code>.
      */
     protected final Set getDefinedHandleObjectIds() {
         final HashSet definedHandleObjectIds = new HashSet (definedHandleObjects
                 .size());
         final Iterator handleObjectItr = definedHandleObjects.iterator();
         while (handleObjectItr.hasNext()) {
             final HandleObject handleObject = (HandleObject) handleObjectItr
                     .next();
             final String id = handleObject.getId();
             definedHandleObjectIds.add(id);
         }
         return definedHandleObjectIds;
     }
 }

